A hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric vehicle, and the like, each need a converter that performs a step-up operation and a step-down operation when a travel motor is driven or a battery is charged. Even for a fuel cell vehicle, the output of a fuel cell is stepped up. One of parts of the converter is a reactor. For example, a reactor has a form in which a pair of coils each having an O-shaped magnetic core and a wire wound on the outer periphery of the magnetic core are arranged in parallel.
PTL 1 discloses a reactor including a magnetic core having an E-shaped cross section, the magnetic core which is so-called a pot core. The magnetic core includes a columnar inner core portion inserted into a single coil, a cylindrical outer core portion arranged to cover the outer periphery of the coil, and a pair of disk-like coupling core portions arranged at both end surfaces of the coil. In the pot core, the coupling core portions couple the concentrically arranged inner and outer core portions with each other and hence a closed magnetic circuit is formed. PTL 1 also discloses that a small reactor can be obtained by increasing the saturation magnetic flux density of the inner core portion as compared with those of the outer core portion and the coupling core portions and hence decreasing the cross-section area of the inner core portion.